It's intentional, like the conflation of capitalism and democracy. It doesn't make sense if any thought is put to it but that doesn't happen enough.

Capitalism refers to economic systems were economic decisions are made by private, rather than public, actors.

The free market is a didactic model of a market with no barriers and no information imbalance.

Capitalism is to broad of a term to say it's different.

Subforms of it may differ (i.e. to my knowledge there is no free market capitalism, although at this point likely better than what especially USA does have...). I'd say free market capitalism is the purest form of it though.

The reality is unfortunately worse (e.g. fossilized energy is still substituted, lobby is much too strong etc. regulations at this point do more damage than good).

And I say all of this as a communist...